The cytochrome P450 proteins (CYPs) are monooxygenases that catalyze reactions involved in both drug metabolism and in the synthesis of cholesterol, steroids and other lipids. P450 enzymes are classified into subfamilies, such as CYP1A and CYP2A, based on their sequence similarities. CYP2A7 (cytochrome P450 2A7), also known as CPA7, CPAD, CYPIIA7 or P450-IIA4, is a 494 amino acid peripheral membrane protein that belongs to the CYP2A subfamily of cytochrome P450 proteins. Localized to the endoplasmic reticulum, CYP2A7 can be induced to high levels in liver in response to foreign compounds, such as carcinogens, pesticides and drugs. CYP2A7 functions as a hydroxylase that uses a heme group to catalyze the oxidation of target flavoproteins.